1. Field of the Invention
The present invention relates to a substrate treatment system, and, more particularly, to a heat-treatment system suitable for processing a substrate such as a semiconductor wafer by an oxidation process for wet oxidation, HCl oxidation or the like, and a gas-treatment system for carrying out a gas-treatment suitable for an oxidation process, a CVD process or the like.
2. Description of the Related Art
A semiconductor device fabricating method includes an oxidation process for oxidizing the surface of a silicon layer in a hot atmosphere of high temperature to form an oxide film (insulating film). A known single wafer processing heat-treatment system capable of processing a wafer by an oxidation process without significantly affecting the heat history of the wafer carries a wafer mounted on a wafer holder to a set position in a reaction tube to process wafers one at a time, and then heats the wafer rapidly.
Referring to FIG. 16 showing such a single wafer processing heat-treatment system, a vertical reaction tube 200 has a section defining a heat-treatment region and surrounded by a heat insulating structure 210. A process gas supply pipe 211 and an exhaust pipe 212 are connected to the reaction tube 200 to cause a process gas supplied into the reaction tube 200 to flow from an upper part toward a lower part of the heat-treatment region.
A wafer holder 220 is disposed in the reaction tube 200. The wafer holder 220 can be vertically moved at a speed in the range of about 150 to about 200 mm/s. A wafer transfer chamber 230 is formed under the reaction tube 200, and a wafer transfer mechanism, not shown, is disposed in the wafer transfer chamber 230. The wafer transfer mechanism puts one wafer W on the wafer holder 220 in the wafer transfer chamber 230, and then the wafer holder 220 raises the wafer W to a predetermined position. Subsequently, a heating unit 240 provided with a resistance heating device 241 and an heat equalizing member 242 heats the wafer W at a predetermined heat processing temperature, and the process gas is supplied through the process gas supply pipe 211 to process the wafer W for atmospheric pressure oxidation.
This single wafer processing heat-treatment system carries out a wet oxidation process using H.sub.2 O gas or an HCl oxidation process using O.sub.2 gas and HCl gas. Since HCl gas is highly corrosive and since a metal member is corroded if HCl gas is used on the metal member wet with water, the reaction tube 200 is made of quartz.
Shutters 250 are disposed between the reaction tube 200 and a vessel defining the wafer transfer chamber 230 disposed under the reaction tube 200 so as to be moved horizontally to isolate and protect the members forming the wafer transfer chamber 230 and a driving mechanism for moving the wafer holder 220 from the corrosive process gases. Semicircular cuts are formed in the shutters 250, respectively, to enable the shutters 250 come into close contact with a lifting shaft 221 for lifting the wafer holder 220. A region extending below a level corresponding to the exhaust pipe 212 and communicating with the interior of the reaction tube 200 is purged with an inert gas, such as N.sub.2 gas.
When processing a wafer W by this heat-treatment system, the wafer W is carried into the reaction tube 200 from below the reaction tube 200. Therefore, the wafer transfer chamber 230, the shutters 250 and the driving mechanism for driving the wafer holder 220 must be disposed below the reaction tube 200, and the heating unit 240 and the heat insulating structure 210 must be arranged outside the reaction tube 200, which inevitably increases the size of the heat-treatment system. Since the reaction tube 200 has a large processing region, the operation for changing the process gas takes much time, which reduces the throughput of the heat-treatment system.
There has been known a heat-treatment system which has a small chamber provided with a heating means like the chamber of a single wafer processing CVD system, and a wafer transfer mechanism capable of carrying a wafer into and out of the chamber through a side wall of a vessel defining the chamber. A single wafer processing CVD system will briefly be described with reference to FIG. 17. Referring to FIG. 17, a cylindrical vessel 260 made of a metal defines a processing chamber and has a side wall provided with an opening 261 through which a wafer is carried into and carried out of the processing chamber. The opening 261 is closed by a gate valve 270. A support table 280 internally provided with a heater is disposed in the bottom region of the processing chamber defined by the cylindrical vessel 260. A heating device 290 is disposed above the support table 280 in the cylindrical vessel 260.
Since the opening 261 through which a wafer W is carried into and carried out of the processing chamber is formed on one side of a processing region as shown in FIG. 18, the condition of a space surrounding the wafer W is affected by the opening 261, and uniformity in heat radiation with respect to the circumference of the wafer W is deteriorated. In a process which subjects the wafer W to a high process temperature, such as an oxidation process, the adverse effect of the deterioration of uniformity in heat radiation is significant and uniformity in oxidation in the surface of the wafer W is deteriorated even if the wafer W is rotated during the oxidation process. Since the cylindrical vessel 260 defining the processing chamber is made of a metal, the cylindrical vessel 260 is corroded if a corrosive process gas is used for the oxidation process.